This invention relates to polypeptide fragments of the Streptococcus mutans I/II antigen that are useful in treating and preventing dental caries.
Streptococcus mutans is the main etiological agent of dental caries, a disease which affects mammals including humans.
The S. mutans I/II antigen (SA I/II) is a cell surface protein with an Mr of about 185 kDa. It is believed to comprise several antigenic epitopes and to be at least partly responsible for S. mutans adhesion to teeth.
SA I/II is described in British Patent No. 2,060,647, as are number antibodies to it. A putative 3.5 to 4.5 kDa fragment of SA I/II, xe2x80x9cantigen Xxe2x80x9d, has also been described in European Patent No. 0 116 472.
However, it has now become clear that xe2x80x9cantigen Xxe2x80x9d is not a fragment of SA I/II at all. Rather, it is a separate protein that merely co-purifies with SA I/II. It is believed to be encoded by a separate gene.
Two large fragments of SA I/II, an N-terminal fragment (residues 39 to 481) and a 40 kDa central fragment (residues 816 to 1213) are recognised by human serum antibodies. Within the central fragment, 80% of the sera tested recognise elements within a proline-rich region (residues 839-955) that comprises three tandem repeats. This suggests that this region includes one or more B-cell epitopes. The central fragment (residues 816-1213) is also believed to comprise one or more adhesion sites that mediate S. mutans"" attachment to the tooth.
The aim of the above-mentioned work has been the development of vaccines for immunisation against dental caries. However, precise identification of the antigenic epitopes within SA I/II is a prerequisite for designing synthetic vaccines based on it. Similarly, precise identification of adhesion sites is essential for the design of drugs against dental caries that rely on inhibiting S. mutans"" adhesion to the tooth.
No antigenic epitopes (T-cell or B-cell epitopes) or adhesion sites within SA I/II have been characterised, nor has the precise location of any such regions been suggested. Also, there has been no indication of the location of S. mutans"" T-cell epitopes as the above-mentioned work has concentrated on S. mutans"" ability to adhere to teeth and to generate a B-cell response.
The inventors have identified a number of T-cell epitopes, B-cell epitopes and adhesion sites within residues 803 to 1114 of SA I/II. Some of the T-cell and B-cell epitopes overlap or are contiguous with each other and/or with one or more of the adhesion sites.
The presence of a number of antigenic epitopes of both types and a number of adhesion sites within the same region of SA I/II could not have been predicted and the finding that some of the adhesion sites and epitopes overlap or are contiguous with each other is particularly surprising.
These findings make it possible to design effective synthetic vaccines against dental caries as well as drugs that engender resistance against the disease or alleviate pre-existing cases of it by preventing S. mutans"" adhesion to the tooth. Further, the surprising finding that some of the T-antigenic epitopes and the adhesion site are contiguous or overlapping makes it possible to design bifunctional drugs that effect immunisation against dental caries as well as preventing adhesion of S. mutans to the tooth.
Accordingly, the present invention provides a nucleic acid sequence which codes upon expression in a prokaryoic or eukaryotic host cell for a polypeptide product having one or more properties selected from (i) the ability to adhere to a mammalian tooth in a competitive manner with naturally occurring Streptococcus mutans antigen I/II, thus preventing or diminishing the adhesion of S.mutans to the tooth; (ii) the ability to stimulate a T-cell response; and (iii) the ability to stimulate a B-cell response, said nucleic acid sequence being selected from:
(a) the sequences shown in SEQ. ID. Nos. 12 to 22 or the complementary strands thereof;
(b) nucleic acid sequences having a length of not more than 1000 base pairs which hybridise to the sequences defined in (a) over at least 70% of their length;
(c) nucleic acid sequences having a length of not more than 1000 base pairs which, but for the degeneracy of the genetic code, would hybridise to the nucleic acid sequences defined in (a) or (b) over at least 70% of their length and which sequences code for polypeptides having the same amino acid sequence code, would hybridise to the nucleic acid sequences defined in (a) or (b) over at least 70% of their length and which sequences code for polypeptides having the same amino acid sequence.